a) Field of the Invention
The present invention relates to a VEGF (Vascular endothelial growth factor) polypeptide that binds to β-amyloid (Aβ). The present invention also relates to a compound that sequesters Aβ. And conversely, the invention relates to a compound that sequesters VEGF. Thus, the present invention also relates to a method of screening for a compound that inhibits the binding of VEGF to Aβ. In addition, the invention relates to a method of preventing and treating Alzheimer's Disease as well as treating excessive angiogenesis.
b) Description of the Related Art
Alzheimer's disease (AD), the most common cause of dementia in elderly people, is a complex disorder of the central nervous system clinically characterized by a progressive loss of cognitive abilities. Pathological hallmarks of AD are extracellular senile plaques, intracellular neurofibrillary tangles, loss of neurons, cerebral amyloid angiopathy, and degeneration of cerebrovasculatures in certain areas of the brain (Marti et al., Proc Natl Acad Sci USA 1998;95(26):15809-15814; Yamada M., Neuropathology 2000; 20(1): 8-22; Yankner B A, Neuron 1996;16(5):921-932). Aβ (Aβ) is the major component of senile plaques and is derived from the amyloid precursor protein by proteolytic cleavage (Vassar et al., Neuron 2000;27(3): 419-422). Although accumulating evidence suggests that Aβ is a key causative agent of AD (Calhoun et al., Nature 1998;395(6704):755-756; Hardy et al., Science 1992;256(5054):184-185; Hsiao et al., Science 1996;274(5284):99-102; Lewis et al., Science 2001;293(5534):1487-1491; Schenk et al., Nature 1999;400(6740):173-177; Sommer B., Curr Opin Pharmacol 2002;2(1):87-92; Thomas et al., Nature 1996;380(6570):168-171), the exact mechanism of neuronal degeneration in AD is not clear. However, it is likely that multiple factors are involved in the development of the disease.
Most cases of AD are accompanied by cerebrovascular pathologies, such as cerebral amyloid angiopathy, endothelial degeneration, and hypoperfusion (de la Torre J C. Stroke 2002;33(4):1152-1162; Kalaria R N. Neurobiol Aging 2000;21(2):321-330; Kokmen et al., Neurology 1996;46(1):154-159; Snowdon et al., JAMA 1997;277(10):813-817; Thomas et al., Nature 1996;380(6570):168-171). Vascular risk factors linked to cerebrovascular diseases and stroke, such as hypertension, atherosclerosis, diabetes mellitus, and cardiac disease, are known to significantly increase the risk of developing AD. Most of these vascular pathologies cause cerebral ischemia that are commonly present in AD patients. These observations suggest that cerebrovascular dysfunction may play an important role in the neurodegenerative cascade of AD.
Vascular endothelial growth factor (VEGF) is a major regulator of blood vessel function including hyperpermeability, endothelial cell growth, and enhanced glucose transport. VEGF also plays a key role in physiological blood vessel formation and pathological neovascularization such as tumor growth and ischemic diseases (Ferrara N. Am J Physiol Cell Physiol 2001;280(6):C1358-C1366; Harrigan et al., Neurosurgery 2002;50(3):589-598; Plate et al., Nature 1992;359(6398):845-848; Shweiki et al., Nature 1992;359(6398):843-845; Zhang et al., J Clin Invest 2000;106(7):829-838). Expression of VEGF and its receptor in various organs including brain is upregulated in response to hypoxic or hypoglycemic stress that are present in AD (Marti et al., Proc Natl Acad Sci USA 1998;95(26):15809-15814; Marti et al., Am J Pathol 2000;156(3):965-976; Stein et al., Mol Cell Biol 1995;15(10):5363-5368).
There are also reports of increased levels of VEGF in the cerebrospinal fluid of AD patients and enhanced VEGF immunoreactivity around perivascular astrocytes and walls of cerebral vessels in subjects with AD when compared with elderly controls (Kalaria et al., Brain Res Mol Brain Res 1998;62(1):101-105; Tarkowski et al., Neurobiol Aging 2002;23(2):237-243). Moreover, VEGF was highly expressed in neuronal and glial cells since cerebrovascular pathologies associated with AD cause cerebral ischemia (Kalaria et al., Brain Res Mol Brain Res 1998;62(1):101-105; Tarkowski et al., Neurobiol Aging 2002;23(2):237-243). However, in these reports, the direct interaction and co-localization of VEGF with Aβ were not established.
Recently, it was reported that VEGF has neurotrophic as well as neuroprotective functions against ischemic and glutamate-induced excitotoxic damage (Jin et al., Proc Natl Acad Sci USA 2000;97(18):10242-10247; Matsuzaki et al., FASEB J 2001;15(7):1218-122P; Ogunshola et al., J Biol Chem 2002;277(13):11410-11415; Oosthuyse et al., Nature Genet 2001;28(2):131-138; Schratzberger et al., Nature Med 2000;6(4):405-413; Sondell et al., J Neurosci 1999;19(14):5731-5740). These studies have raised the possibility that VEGF may be involved in the vascular and neuronal pathology associated with AD. The present application describes the heavy accumulation and co-localization of VEGF with Aβ plaques in the brain of patients with AD. In vitro experiments show that VEGF binds to Aβ with high affinity and is co-aggregated with Aβ. Once bound, VEGF is released from the complex at a very slow rate.
There is a need in the art to provide more accurate and sensitive molecular tool to detect the presence of Aβ formation and aggregation so that neural diseases such as Alzheimer's Disease can be detected early and treated. In addition, there is a need in the art for a compound that inhibits VEGF binding to Aβ so that VEGF is free to carry out its neuroprotective and neurotrophic activity in the brain.